"Following on from the railways, it now appears he is facing severe problems in aviation. Just like the crisis on the railways and London Underground, it is clear these problems will not be resolved until Byers stands aside."

Liberal Democrat Tom Brake said: "Part-privatisation of air traffic control was always going to be more insecure than an organisation fully backed by the Government.

"The Government should have created a not-for-profit company at the outset. It would have been able to raise the &#xA3;1 billion needed for investment through Government-backed bonds."

The row over Nats broke out as a troubled Mr Byers was still reeling from a string of embarrassing foul-ups.

He has faced calls for his head after the botched take-over of Railtrack and a series of rail strikes that have seen the nation's system grind to a halt.

And today strike-plagued rail firm Arriva, which runs services across the North East, was carpeted by advertising watchdogs and told not to repeat `misleading' claims that it was offering passengers an `efficient' service.

In its response to the Advertising Standards Agency, Arriva Trains said the claim, made in an advert for a technical auditor, was only `aspirational.'

More Metro misery was also on the cards for Tyneside commuters after drivers' union Aslef rejected a 3.8 per cent pay offer from Nexus chiefs.

Strikes due to take place today had already been suspended but Aslef members will begin voting on new industrial action at the end of the week.